The invention relates generally to systems for protecting spacecraft from hazardous space plasma environment, and more specifically it relates to a new kind of system for the mitigation of spacecraft surface charging using polar molecules. There exists a class of polar molecules which are electro-negative. This class includes the halocarbons, and includes the fluorocarbon refrigerants. They readily pick up electrons and become negatively charged molecules. In this invention, neutral polar molecular liquid is sprayed in fine mist form onto negatively charged spacecraft surfaces. The molecules pick up the electrons and evaporate away with the electrons.
Charging of spacecraft in the space plasma environment may be hazardous to the health of on-board electronics. It may affect telemetry, navigation, operations, and even the survivability of spacecraft, and degrade scientific measurements. Spacecraft charging may be due to natural or artificial causes. Natural charging is due to the interaction between a spacecraft and its space plasma environment. Artificial charging is due to beam emissions, for example. In the geosynchronous environment, a spacecraft is often charged negatively during eclipse.
The task of providing spacecraft charging protection using technology is alleviated by the following U.S. Patents, the disclosures of which are incorporated herein by reference:
U.S. Pat. No. 5,594,325 issued to David Manner;
U.S. Pat. No. 4,691,159 issued to Ahrens et al.;
U.S. Pat. No. 4,899,269 issued to Rouzies;
U.S. Pat. No. 5,394,075 issued to Ahrens et al.;
U.S. Pat. No. 5,444,358 issued to Delepaunt;
U.S. Pat. No. 5,451,858 issued to Van Duyne et al.
The above-cited references describe patented space radiation protection systems. The Manner patent describes the use of spacecraft power systems to mitigate spacecraft charging effects. Geosynchronous spacecraft have a history of charging anomalies. Conventional passive protection measures are often complex and costly.
The present invention is a system for mitigating spacecraft charging by means of polar molecules. A polar molecule is a molecule possessing a permanent electric dipole moment. Molecules containing atoms of more than one element are polar except where forbidden by symmetry; molecules formed from atoms of a single element are nonpolar.
The present invention is based on the theory that the positive ions returning to the spacecraft neutralize the excessive negative surface charge and the electrons leaving from the spacecraft carry away negative charge. Using ions or electrons alone would cause differential charging, meaning different surfaces attaining different charging levels. On one embodiment of the invention a polar molecule liquid is stored in a container. A heating coil is inside. The heater coil is capable of heating the liquid to temperatures near boiling. The liquid flows along a tube through a control knob to atomizer sprayer, which is mounted on a movable arm on a tower. The lengths of the towers and arms equal the radius of the spacecraft approximately.
To operate the device, the movable arm moves into a desired position to aim the polar liquid vapor/droplet spray onto a charged spacecraft surface. The vapor/droplets are neutral initially. There the droplets act as electron scavengers and become negatively charged droplets. As they evaporate to small sizes, they eventually burst into smaller droplets taking the electrons away.
The control knob can be switched on or off by a remote command from the ground. When the negative charging level of the spacecraft or a spacecraft surface reaches a certain level, the ground command can optionally turn the mitigation device on. When the level falls to a certain level, the ground command can optionally turn the mitigation device off. Alternatively, it can be turned on or off automatically by linking it to a charge sensor. When the sensor senses a critical charging level, it can send a command to turn on or off the device automatically.